Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
J~ 3~
A Multidirectional Feed And F1ush-~o~nted
Surface Wave Antenna
Technica~ Field
The present invention relatec; to a
multidirectional feed which can be used by itself or
incorporated within a surface-wave structure to form for
example, a flush~mounted antenna on a mobile unit. More
particularly, the present invention relates to a
multidirectional antenna feed comprising an annular
slot, and associated cavity, in a ground plane which
slot area is fed by multiple, spaced-apart, connections
from, for example, a coaxial line. The feed further
comprises a cavity designed for both shielding radio
waves excited in the annular slot and cavity from
propagating in a direction opposite an aperture of the
slot and preventing a shorting of the radio waves. The
feed generates a multidirectional radio wave that can be
launched into a surface wave antenna structure which can
be flush-mounted in the outer surface of a mobile unit
to provide uniform radiation in azimuth in all
directions with moderate elevation gain. The multiple
connections can further be individually fed with varying
amplitudes and phases to provide multi-lobed azimuth
radiation for diversity operation.
Description of the Prior Art
Antennas for vehicles or aircraft have been
provided in various con~igurations. The most general
one seen -today for vehicles is the whip antenna as
disclosed, for example, in U.S. patent 4,0a9,817 issued
to D. Kirkendall on May 16, 1978~
Slot antennas have also been ~sed for mobile
radio communication and can be found comprising many
different forms. In U.S. patent 2,644,090 issued to
- 2 ~ 7~
~. Dorne on June 30, 1g53, a recessed slo~ antenna ~or
an aircraft is disclosed which comprises either an
annular slot in a conducting surface or an annular slot
arranged in four arcuate slot sections in a conducting
surface separated by conductiny strips extending
transversely across thel s]ot. A shallow cavity i~
formed below the conducting surface ~ out,Jardl~
extending walls and the cavity is centrally fed by a
coaxial lineO
~.S. patent 3,631,500 issued to K. Itoh on
December 2~ 71, discloses a mobile radio slot antenna
comprising a slot in a conducting plate and an electric
current antenna normal to the plate. The signals from
each antenna are independently coupled to separate
square law detectors and combined to provide the output
signal.
Another mobile radio slot antenna is disclosed
in U.S. patent ~,443,802 issued to P. Mayes on April 17
1984, wherein a hybrid slot antenna comprises a pair of
closely spaced parallel ground planes and a radiating
element which is a composite aper~ure formed into the
upper ground plane. One portion of the radiating
element is a long narrow slot and the other portion is
an annular slot coincident with the narrow slot.
Electromagnetic energy is conveyed to and from the slots
by means of a feed parallel to, and sandwiched between,
the two ground planes.
Another annular slot antenna arrangement is
disclosed in Antenna ~ngineering ~landbook by H. Jasik,
E`irst Edition, Mc~raw-Hill in FIG. 27-4~ at page 27-36.
There the antenna comprises an inner parasitic annular
slot and an outer driven annular slot. The parasitic
annular slot and associated cavity is coupled to the
radiating aperture through a mutual impedance between
the two slots. The cavities associated with the outer
driven annular slot are shaped to provide an equivalent
parallel tuned circuit and provide a low characteristic
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impedance to the centrally ~ed coaxi~l Iine.
The problern in the prior art is to ~rovide a
mobile antenna which pravides all of the electromagnetic
performance requirements of a mobile telephone antenna
while remaining conformal to the surface o~ a vehicle.
Such antenna should provide a uniform azimuthal pattern
and elevation gain in the horizontal direction with a
wide-band efficient feed that is simple and inexpensive
to implement and is less susceptible to dama~e or
vandalism and burglary than prior art mobile antennas.
Summar~ of the Invention
The foregoing problem has been solved in
accordance with the present invention which relates to 3
multidirectional feed for an antenna which can be
flush-mounted with the outer surface of a mobile unit.
More particularly, the present invention relates to a
multidirectional annular slot antenna feed comprising an
annular slot and an associated cavity in a ground plane,
where the slot is fed by multiple, spaced apart,
connections from, for example, one or more coaxial lines
to excite radio waves in the annular slot and associated
cavity. The cavity provides for both shielding the
radio waves from propagating in a direction opposite to
the aperture of the annular slot and preventing a
shorting of the radio waves. The multiple connections
can further be individually fed with varying amplitudes
and phases to provide multi-lobed azim~th radiation for
diversity operation.
It is an aspect of the present invention to
provide a feed that generates a multidirectional radio
wave that can be launched into a surface-wave antenna
structure to provide uniform or multi-lobed radiation in
azimuth with moderate elevation gain. The feed
comprises an annular slot, and an associated cavity,
connected to an associated transceiver by, for example,
a coaxial line coupled to multiple, spaced-apart, points
around the slot. The cavity has its inner wall formed
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from a conductive material to shield the radio waves
excited in the slot from propagatiny in a direction
opposite the aperture of t'ne slot and a wid~ch to prevent a
shorting of the radio waves. The Eeed can be mounted by
5 itself or within a surface wave structure in Jche outer
surface of a mobile unit. The optional surface wave
structure can comprise any combination of corrugations and
a layer of dielectric material. If the feed and optional
surface-wave structure are disposed in a slight depression
10 in the outer surface of the mobile unit, a dielectric
layer, forming part of the surface wave structure, can
fill in the depression to conform with the outer surface
of the mobile unit.
In accordance with one aspect of the invention
15 there is provided a multidirectional antenna feed
arrangement comprising: a ground plane including an
annular cavity within the ground plane comprising a width
between inner walls which approximates a
~uarter-wavelength o a radio wave to be launched or
20 received by the antenna feed arrangement to prevent a
shorting of the radio wave within the cavity, and an
annular slot forming an opening from the cavity in a first
major surface of the ground plane; and means, disposed at
multiple spaced-apart locations around a first edge of the
25 annular slot, and capable of simultaneously delivering a
radio frequencey message signal to multiple locations
around the annular slot for exciting a corresponding radio
wave in the cavity and slot and launching said radio wave
from the slot.
Other and further aspects of the present
invention will become apparent during the course of the
following description and by reference to the accompanying
drawings.
~3rief Description of the Drawings
Referring now to the drawings in which like
numerals represent like parts in the several views:
- 4a - ~ 7~
FIG. 1 is a cross-sectional side view of an
annular slot antenna feed illustratiny the yeneral concept
of the present feed arrangement;
FIG. 2 is a cros.s-sectional view of a pre~erred
embodiment of an annular slot antenna feed in accordance
with the present invention, which embodiment is similar to
the arrangement of FIG. 1, including a surface wave
structure and is flush-mounted with the surface of a
mobile unit;
FIG. 3 is a partial cross-sectional view in
perspective of the feed arrangement shown in FIG. 2;
FIG. 4 is a partial view in perspective of the
underside of the feed arrangement shown in FIG. 3;
FIG. 5 is a cross-sectional side view of the
interconnection arrangement between the stripline and
conducting layer forming the annular slot of the
arrangement of FIGS. 2-4;
- 5 - ~ ~5~7~)~
FIG. 6 is a partiaL cross-sectional side ~iew
of the arrangement of FI~. 2 which includes a corrug3ted
surface wave structure;
FIG. 7 illustrates the mounting of the presen~
feed arrangement in the roof of a vehicle; and
FIG. 8 is a partial view in perspective of the
underside of the feed arrangement shown in FIG. ~ with
individual leads to each point of launch or reception
around the annular cavity and diversity switching means.
Detailed Description
FIG. 1 is a cross-sectional side view of a
basic version of a feed and surface wave antenna
arrangement in accordance with the present invention to
aid in providing an understanding of the concepts
involved. In FIG. 1, a ground plane 10 of conductive
material is formed to include an annular cavity 11,
which is filled with a dielectric material, that opens
into an annular slot 12. An input feed 13, as, for
example, the coaxial line shown in FIG. 1, has the
shield thereof grounded to ground plane 10 while the
center conductor thereof is coupled by wires 14 to
multiple points around annular slot 12 through apertures
15 in both ground plane 10 and the dielectric material
in cavity 11. It is preferred that the multiple points
of connection to annular slot 12 be three or more in
number if it is desired to ensure uniform radiation in
azimuth in all directions from the feed. It is to be
understood that an increase in equally-spaced
connections around annular slot 12 provides a more
uniform radiation in azimuth in all directions, and that
the path lengths of feed line 13 to the multiple point
connections around annular slot 12 should preferably be
of equal length for uniform radiation.
The Eeed arrangement can be disposed in a
depression in the outer surface 16 of a mobile unit and
the depression filled with a dielectric material 17 to
form a surface wave propagating device which results in
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a flush-mounted antenna arrangement. Annular ca~/it~
preferably should have (l) its inner surface forrned with
a conductive layer to prevent radio ~"aves excited in
annular slot 12, and in turn cavity ll, from propagatiny
in a direction away from annular slot 12, and (2) a
width to prevent shorting of the radio waves in cavity
ll. More particularly, the width of cavity ll should
approximate a quarter-wavelength so that cavity ll will
appear close to an open circuit. Primarily, the
capacitive reactance provided by annular slot 12 will be
then balanced out by the inductive reactance provided by
the approximate quarter-wavelength width of cavity ll
and thereby prevent a shorting of the radio waves in
cavity ll. Additionally, annular slot 12 preferably
should include a spacing of approximately one-tenth
wavelength or less, but it should be understood that
such slot width is not a definite limitation and could
be increased somewhat for purposes of practicality and
still provide proper operation.
In operation, an r-f signal is coupled through
feed line 13 to its multiple connections around and
adjacent annular slot 12, or the various connections
could be fed independently as shown in FIG. 8. In this
regard see, for example, the article "Generalized
Transmission Line Model for Microstrip Patches" by A. K.
Bhattacharyya et al. in IEE Proceedings, Vol. 132, Pt.
H, No. 2, April 1985, at pages 93-98. The r-f signal is
excited in annular slot 12 and cavity ll. The cavity
includes an inner wall that is formed from a conductive
material and, therefore, prevents the excited radio wave
from propagatin~ past the bottom of the cavity. The
cavity also has a width to prevent the radio wave
excited in cavity from being shorted therein. ~s a
result, the radio wave is launched from annular slot 12.
A surface wave device 17 can be provided to launch the
radio wave with uniform or multi-lobed radiation in
azimuth and with moderate elevation gain.
-
FIG. 2 illus~rates a cross-sectional side vie,
of a preferred embodiment of the present feed
arrangement, which is similar to the arrang2ment of
FIG. 1. In FIG. 2 yround plane 10 is provided with an
annular channel therein forming cavity 11. Cavity ll,
or the channel, is filled with a ring of dielectric
material. A layer 18 of conductive material is formed,
or disposed, over the ring of dielectric material by any
well-known technique. It is to be understood that
conductive layer 18 can comprise any conductive
material, including that of ground plane 10, and can be
formed, for example, by disposing a ring of the
conductive material over the dielectric material in
cavity 11, with the inner edge of layer 18 making
electrical contact with ground plane 10. Alternatively,
conductive layer 18 could be formed on both the
dielectric material in cavity 11 and all or part of the
central upper surface of ground plane 10 surrounded by
annular cavity 11. A portion of layer 18 can then be
removed, as required, by machining or etching techniques
to form annular slot 12 adjacent the outer rim of
cavity 11.
Instead of a coaxial cable as shown in FIG. 1,
feed 13 is shown in FIG. 2 as comprising an
appropriately dimensioned stripline 19 or other layer of
conductive material disposed in a groove 20 in ground
plane 10. Stripline 19 is shown insulated from ground
plane 10 by an insulating layer 21~ Stripline 19 is
further shown as connected to conducting layer 18 by
wires 14 or other means (e.g, plated through hole, etc)
passing through apertures 15 at ~ultiple locations
around annular slot 12. ~ cover 23 of preferably
conductive material, similar to ground plane 10, is
disposed to cover (1) the striplines 19 and associated
grooves 20 in ground plane 10 and (2) the bottom of
ground plane 10.
7~
Ground plane 10 also can incl~de an annular
recess 2~ around its upper outer edye to permit mountin~J
of the feed arrangement in an aperture ~5 in the outer
surface 16 oE a mobile ~nit. A layer 17 o~ dielectric
material can then be disposed over the ground plane 10
and the adjacent outer surface 16 of the mobile unit
mounting the feed to form a surface wave structure which
can be formed flush with the outer surface 16 of the
mobile unit. It i5 to be understood that the feed
arrangement can ~e permanently mounted to the outer
surface 16 of the mobile unit at recess 26 with, for
example, screws or tack welds (not shown). Similarly,
cover 23 can be joined to ground plane 10 by means Gf,
for example, screws or tack welds (not shown).
FIG. 3 is a partial cross-sectional top and
side view in perspective of the feed arrangement of
FIG. 2, without cover 23, to provide a clearer
perspective of the feed arrangement. As can be seen
from this view, and that of FIG. 4 which is a bottom and
side view of the feed arrangement of FIG. 3, stripline
feed 19 comprises a main feed which is connected to a
transceiver via a coaxial line 27. The main feed then
branches off into two sections at the middle of ground
plane 10 and then subdivides in each branch to provide
2S four equally spaced connections via wires 14 to annular
slot 12. Other and similar arrangements could be
provided for other numbers of multiple connections to
annular slot 12 which preferably should be three or more
connections if it is desired to assure a uniform
- 30 launching of a radio wave in all directions from annular
slot 12.
FIG. 5 shows an enlarged cross-sectional view
of the feed arrangement of FIGs. 2-4 in the area of
annular slot 12, depicting the interconnection of a
stripline feed 19 through insulating layer 21, ground
plane 10, and the dielectric material in cavity 11 to
the layer 18 with a wire 14. In FIG. 5, the wire 14 is
~ 9 ~
electrically connected to layer 18 and stripline lg b~ a
solder connection 29. ~lso shown is a la~er of
insulating material 28 ~hich i5 disposed in gro~ve 2()
between stripline 19 and cover 23 to prevent a possible
short therebetween.
FIG. 6 illustrates an enlarged partial cross
sectional side view of the arrangement of FIG. 2 and 5
to provide a corrugated surface wave device adjacent
annular slot 12 in the upper surface of ground plane 10
and the outer surface 16 of the mobile unit. To provide
such corrugated surface wave device, the upper surface
of ground plane 10 and the dielectric material in cavity
11 is formed with corrugations 30 of a predetermined
width and depth. In a similar manner, the outer surface
of the mobile unit, in the vicinity of the feed, is also
formed with corrugations 30 of said predetermined width
and depth to permit a surface wave of the r-f
transmitted or received signal to propagate therealong
to and from annular slot 12. Corrugations 30 would
preferably be annular in nature and progress outwards
from the center of the feed and into the outer surface
16 of the mobile unit mounting the feed. The annular
progression of corrugations 30 permit a surface wave to
propagate uniformly out from annular slot 12 in azimuth
in all directions and similarly permit the feed to
receive radio waves from all directions in azimuth. As
is well-known in the art, the depth of corrugations 30
should approximate a quarter wavelength. The shape of
the corrugations 30 can comprise any shape as, for
example, rectangular, etc. Depending on the shape, it
may also be advantageous to add a layer 17 of dielectric
material to fill in corrugations 30, as shown in FIG. 6,
to (a) provide a more efficient surface wave device, (b)
allow the use of shallow corrugations, and (c) provide a
smooth contour with the outer surface 16 of the mobile
unit especially if, for example, the feed arrangement of
FIG. 2 is mounted in a depression in the outer surface
- 1 o ~ 7(~
16 of the mo~ile unit.
FIG. 7 illustrates a typical roof mounting
arrangement of the present feed and antenna arrangement
in a vehicle. There the feed arrangement 10 of
FIGs. 2-6 is mounted in a depression in the roof, and a
corrugated and/or dielectric layer surface wave device
17 fills in the depression to provide a flush-mounted
antenna arrangement. A coaxial cable 27 to the feed
arrangement can be run to the associated transceiver in
the mobile unit between the roof (outer surface 16) and
a head-liner 31 of the vehicle. As shown in FIG. 8, for
diverslty operation, the multiple connections around
annular cavity ll can be individually fed via leads 40
to each of the points about annular cavity 11 to produce
multi-lobe radiation which matches a channel radiation
pattern appropriate of the local environment. More
particularly, the amplitudes and phases of the signal
for each of the multiple points about annular cavity 11
should be the complex conjugate of the transmission
coefficient from that port or point to the remote base
station for adaptive maximal ratio diversity operation.
For switched diversity operation, the portable receiver
or transmitter is sequentially switched via switching
means 41 between each of the multiple points or ports
about annular cavity 11 until the strongest signal is
obtained. Such switched diversity operation is well
known in the art as shown and described in, for example,
the book Microwave Mobile Communications, by W. C.
Jakes, J. Wiley and Sons, 1974, at pages 401 402.
It is to be understood that the above-
described embodiments are simply illustrative of the
principles of the invention. Various other
modifications and changes may be made by those skilled
in the art which will embody the principles of the
invention and fall within the spirit and scope thereo~.
For example, ground plane 10, and cover 23, could be
fabricated from a light-weight dielectric material
- 1 1 - 1~5~7()f~
(e.g~, foam, etc.) and the complete outer surface
thereof, including cavity 11, formed with a thin layer
of conductive material to reduce the weight of the
overall antenna feed arrangement. With such fabrication
technique, one could avoid forming a conductive layer
both within grooves 20 associated with stripline feeds
19 and on cover 23 either totally or just adjacent
grooves 20. Such latter arrangement would then not
require the insulation layers 21 and 28 on either side
of striplines 19.
